During the production of coverings of the type specified above, problems arise in connection both with the appearance of the covering and with requirements of a technical and structural nature such as, for example, the need to produce a covering with good resistance to mechanical stresses, for example, to bending, or the need to ensure that the covering has good dimensional stability.
With regard to this latter aspect in particular, it has been found that rubber-based coverings produced in conventional manner by a calendering operation may show physical and mechanical characteristics which are not isotropic since they are influenced by the direction (longitudinal or transverse the direction of working) in which the measurement is made.
Without wishing to be bound to any specific theory in this connection, there is reason to believe that this is due to a xe2x80x9cstretchingxe2x80x9d effect on the granules in the direction of calendering, this effect being intrinsic in this operation.
The deformation or stretching of the granules which is in any case brought about by the calendering may also have the disadvantage of giving the appearance of the covering a directional character, rendering the direction of calendering recognizable upon optical inspection of the covering.
The object of the present invention is to provide a method which permits the production of a rubber-based covering having excellent structural properties both with regard to resistance to deformation and with regard to dimensional stability, and the aesthetic characteristics of which can be modified with considerable flexibility according to requirements and taste.
In this connection, it is important to stress that the present invention relates to rubber-based coverings (with the meaning specified below) and, from this point of view, is distinguished from techniques relating to the manufacture of coverings based on thermoplastic materials (such as, for example, PVC, polyolefins or so-called thermoplastic rubbers which are actually constituted by a polyolefin matrix in which a vulcanized rubber phase is finely dispersed). In this field, current practice is to produce a bed or mat of granules which is then subjected to a hot rolling process usually having the character of a calendering operation. The softening of the granules thus brought about causes the formation of a continuous sheet. Naturally, the above-described intrinsic disadvantages of calendering remain.
According to the present invention, the object indicated above is achieved by means of a method of producing rubber-based coverings having the further specific characteristics recited in the following claims. A further subject of the invention is the intermediate and final products of the method which are distinguished by the basically non-directional (isotropic) nature of their physical, mechanical and aesthetic characteristics.